Normal and abnormal extraocular muscle will be examined in serial sections of the Epon-embedded tissue as a whole. The procedure provides for light microscopic examination of thick sections for the detection of areas of interest. Selected thick sections are reembedded for further examination at the electronmicroscopic level, in either the transverse or longitudinal plane of section of the muscle fibers: correlated sectioning of the same fiber in transverse and longitudinal planes is enabled, as well. In normal muscle we plan to quantify differences of mitochondrial and sarcoplasmic reticulum content among the respective fiber types, as well as along the length of the selfsame fibers which have been previously observed to vary morphologically in a systematic manner. Such morphometric analysis will made with the use of an electronic digitizer planimeter. In abnormal muscle we plan to study the muscle of rats in which a myotonic dystophy syndrome has been induced by the administration of diazacholesterol, as well as rats in which the myotonic symptoms have fully receded upon cessation of drug adminstration. The emphasis will be on ascertaining whether or to what degree the innervational mechanism may be involved in this syndrome.